As is well documented and known, high molecular weight polymers which are cationic, non-ionic, anionic or polyamphalytic in nature have found extensive use in the liquids-solids separation field. More specifically, these polymers have been used extensively either alone or in combination with other aids in the flocculation or coagulation of water-insoluble particles suspended in an aqueous medium.
As an off-spring of the use of these polymers in the influent and effluent water of industrial, domestic and agricultural water systems, these polymers have been used in the dredging operations. However, the degree of success in the latter operation has been quite limited in both performance and economy.
The polymers when used as flocculating agents are utilized as solutions with varying degrees of concentration. High molecular weight polymers, although effective as flocculating agents, have a definite disadvantage in that only small concentrations (0.25 to 5%) of such can be produced and to accomplish this generally requires expensive and sophisticated equipment. Numerous methods and various equipment designs have been proposed and in some cases developed for this purpose with limited success. The successful apparatus has been very large, complex, and expensive. These aspects of the technology have limited the use of these polymeric materials significantly. The polymers used for these purposes described, generally have molecular weights of from about 800,000 to 20,000,000. Accordingly, these sophisticated molecules, because of their high molecular weights, are not easily dissolved so as to produce concentrated solutions. They have in actuality rather limited solubility from a handle-ability standpoint since the ultimate solutions have viscosities which are quite high and therefore not easily handled or pumped. In fact, 0.5% solution of a polymer having a molecular weight of 8,000,000 resembles a gel and, as can be appreciated, the viscosity made such virtually unusable for the purpose.
When attempts were made to utilize these polymeric solutions in dredging operations, great difficulty was experienced in feeding the necessary amounts since it was difficult to mix the necessary amount within the time frame allowed. The output of the pumps used to propel the aqueous medium frequently has capacities to move from 5,000 to 60,000 gallons of aqueous medium per minute. These systems are designed to produce highly turbulent flows in order to maintain the dredge material in suspension. It was also discovered that when attempts were made to feed the polymer solutions, the polymers did not operate effectively and that even with the amount of polymer feed increased, only a small increase in effectiveness was experienced. It is believed that the shearing action experienced by the polymers drastically affects the chain length, i.e., molecular weight.
The objective of feeding polymers to the aqueous medium being pumped is to affect more rapid and more complete flocculation of the suspended matter at the location where the dredged material is placed into the container of a barge, or what is referred to as a dredge material containment area.
It would be most desirable to have flocculants which perform effectively under these rather drastic, abrasive and rapid pumping systems, since dredging operations have been under the careful scrutiny of the Federal, State, and Municipal Environmental Protection Agencies. With most dredging operations, there is a certain amount of suspended matter, such as silt, which does not readily settle in the containment area. The dispersed silt obviously effects not only the aesthetics and utilability of the body of water, but also can effect marine life in general. Accordingly, the authorities have been quick to regulate dredging operations to assure that the environment is fully protected.
The present inventors, while working in this area and after having been only moderately successful with the feeding and use of liquid polymeric flocculants, decided that if flocculents were to be utilized with any degree of success, certain techniques for feeding polymeric materials had to be devised in order to avoid the costly problems inherently experienced and to allow for the obtention of the ultimate effectiveness of the flocculants.